MM-Wave Dielectric setup

There is uncertainty about the dielectric constant of substrates such as silicon at W-band frequencies. Silicon dielectric uncertainty effect becomes very important for the design and simulations of RF circuits and antennas on silicon substrates. Designing an antenna on a substrate with inaccurate value of dielectric constant will change antenna performance and shift the resonance frequency in practice which causes large discrepancies between simulated and measured results. Simple and applicable methods for measuring the permittivity of the substrate are always in great interest of the microwave circuit and antenna designers. There are various methods for measuring dielectric constant including dielectric waveguide, cavity resonator, open resonator and free space method which is more suitable for wide band measurement. Below is the setup for Silicon dielectric constant method based on free space method.

Using amplitude and phase information it is possible to derive both real and imaginary parts of dielectric constant. However, it is possible to derive only the real part just using the phase information of either transmitted or reflected signal. In this work, two approaches are applied to bring out the real part of silicon dielectric constant based on transmission and reflection type measurement method. Note that no calibration and time domain filtering is utilized in the measurements. The transmitter and receiver antennas which are used in the measurement set-up have wide beamwidth far away from Gaussian beam. Only the phase information of the transmitted signal is used to determine the real part of the permittivity.Below is a sample measured data from the setup.